For sure, ReVanced is complicated. But that only serves to reinforce my point, which was that adblocking YouTube on mobile is hard. I only brought it up myself to stop people "um actually"ing me and pointing out that ReVanced exists.
Then, you need to uninstall YouTube
Fwiw, no you don’t. I have both ReVanced and the standard YouTube installed right now, precisely because of the casting issue you mentioned.
My experience has been a little different though. Mine had the cast icon until I went in and specifically turned it off. Which I did because casting doesn’t work. It didn’t work for most of the life of the old YouTube Vanced either. Unfortunately it just seems like Chromecast compatibility is harder for them to replicate through the hacked YouTube client.